Device and system for recording the motion of a wafer and a method therefrom

ABSTRACT

The invention provides a device that can be used to record the motion of a wafer and fine perturbations and vibrations in its motion during its progress through and between semiconductor process and inspection machines in the course of the actual manufacturing process or during a test cycle of the processing or inspection machine. It also provides a system and a method which uses this record mechanical malfunction of the processing or inspection machine which has caused, or could cause, defects in the manufactured wafer whether directly or indirectly.

This application claims priority to International Patent Application No.PCT/IL02/00975 filed on Dec. 4, 2002, which claims priority to IL PatentApplication No. 147692 filed on Jan. 17, 2002.

FIELD OF THE INVENTION

The present invention is related to the field of manufacturing ofsemiconductor devices. Specifically the invention relates to thedetection, measurement, and determination of cause of mechanical stressapplied to semiconductor wafers and related devices during theirhandling by process and inspection machines.

BACKGROUND OF THE INVENTION

Equipment used in the microelectronics industry, commonly consists ofone or more processing chambers. During the manufacturing process, thesilicon wafer is moved through various processing steps and chambers, byuse of wafer handling devices such as robots, elevators, indexers, etc.Mechanical stress—scratches, shock or vibration—applied to the wafersduring their handling by semiconductor processing machines may generatescratches on one of the surfaces of the wafer, lead to the creation ofparticles in the processing chamber that interfere with the productionprocess, cause other defects on the surface of the wafer, or may evenresult in breakage of the wafer.

The scratches or shocks can be caused by bad adjustment of the handlingdevices or by mechanical parts coming in contact with the wafer or othermechanical parts inside the processing machine during the transfer ofthe wafer from one position to another within the processing machine.Shocks can also occur when the robot arm picks up the wafer or releasesit to or from a docking station. Excessive vibrations during wafertransfer can occur as a result of many types of mechanical problem suchas a defective motor or ball-bearing. Shocks and excessive vibrationscan also occur when a cassette containing wafers is transferred from oneprocessing machine to another.

Scratches on the front side of the wafer may destroy dies, directly orby impact of particles released from the surface of the wafer. Scratcheson the back of the wafer may cause breakage of the wafer or contributeto other malfunctions. For instance, as a result of scratches on theback of the wafer, the wafer may be positioned out of focus during thelithography steps of the manufacturing. The damage may appear long afterthe defective stage; and, in such a case, it may take extensive effortsto identify the defective machine. Excessive shocks and vibrations maycause similar problems and their causes may be even more difficult toisolate.

The detection and/or measurement of mechanical stress or impact and thedetermination of its cause are currently difficult and costly. In manycases, the disassembly of the processing machine is required to detectmechanical problems or determine the cause of mechanical problems. Thisresults in conditions that may be very different from those existingduring actual operation of the machine. These differences arise for manyreasons including, for example, the fact that most machines processwafers under vacuum conditions.

U.S. Pat. Nos. 5,444,637 and 6,140,833 describe devices for monitoringparameters that are important in the manufacturing process such as:temperature, current, voltage, radiation, distance of the wafer surfacefrom masks and other parts of the apparatus, concentration of variousgases, etc. These patents describe wafers which have one or moresensors, electronic circuits, and memory devices formed on theirsurfaces by standard techniques. These wafers are placed in theprocessing machine and record the relevant data during the operation ofthe machine. After the process is completed, the data is read from thememory and used to confirm correct operation or suggest adjustments ofthe measured parameter.

Neither of these or other existing devices or methods, however, is ableto provide convenient means for pinpointing the mechanical malfunctionsof the processing machine that are the cause of defects in themanufactured wafer.

It is therefore a purpose of this invention to provide a device that canbe used to record the motion of a wafer and fine perturbations andvibrations in its motion during its progress through and betweensemiconductor process and inspection machines in the course of theactual manufacturing process or during a test cycle of the processing orinspection machine.

It is another purpose of this invention to provide a system and a methodwhich uses a record of the motion of a wafer and fine perturbations andvibrations in its motion during its progress through and betweensemiconductor process machines in the course of the actual manufacturingprocess or during a test cycle of the processing or inspection machineto detect, locate, and identify any mechanical malfunction of theprocessing or inspection machine which has caused, or could cause,defects in the manufactured wafer whether directly or indirectly, as forinstance, by releasing particles in the processing chamber.

Further purposes and advantages of this invention will appear as thedescription proceeds.

SUMMARY OF THE INVENTION

In a first aspect the present invention provides a device for recordingthe motion of a wafer, including fine perturbations and vibrations inthe motion of the wafer, during its progress through and betweensemiconductor process and inspection machines in the course of theactual manufacturing process or in test cycles of the machines. Thedevice of the invention comprises a test wafer to which a miniatureelectronic recording system is attached. The electronic recording systembeing provided with memory means for storing information relative to thephysical history of the wafer, and means for connecting to downloadingconnections through which the stored data can be transmitted to anexternal device.

The test wafers can have surface areas and shape, thicknesses, andweights essentially equal those of standard size production wafers orsurface areas and shape essentially equal those of standard sizeproduction wafers but thicknesses and/or weights which differ from thoseof standard size production wafers. The test wafers are made frommaterials including silicon, aluminum, glass, gallium arsenide, ceramicmaterial, or plastic.

The miniature electronic recording system is attached to the test waferby gluing, screwing, or bolting. In a preferred embodiment, thecomponents of the miniature electronic recording system are mounted onone or more circuit boards.

The miniature electronic recording system can be covered by an epoxyblock molded on the surface of the wafer or by a thin hermetic externalcover such the maximum thickness of electronics and cover is not morethan 2 mm. The hermetic thin casing is made of, for example, aluminum,stainless steel, composite materials, polyurethane, silicon, ceramicmaterials or plastic.

The components of the miniature electronic recording system are selectedfrom accelerometers, analog-to-digital converters, microprocessors,batteries, memory units, temperature sensors, and additional standardelectronic components. The accelerometers are of many types including:dual-axis accelerometers, 3-axis accelerometers, and piezoelectric typeaccelerometers. The analog-to-digital converter includes an analogmultiplexer which enables the digitizing of a multitude of analogsignals. The microprocessor includes a real-time clock and internalprogram memory. The battery can be a lithium polymer rechargeablebattery or a non-rechargeable battery. The memory unit is composed ofRAM memory and/or Flash memory.

Additional sensors can be attached to the test wafer. These sensors aresuitable for measuring temperature, light, pressure, air-flow, gas flow,humidity, clearance, electric fields and magnetic fields. A miniaturecamera can also be attached to the test wafer.

The miniature electronic recording system can conserve power bydetecting the motion of the test wafer to which it is attached and usingthe presence or absence of such motion to switch off or wake up theelectronics.

In a second aspect, the present invention provides a system, whichrecords the motion of a wafer, including fine perturbations andvibrations in the motion of the wafer, during its progress through andbetween semiconductor process and inspection machines in the course ofthe actual manufacturing process or in test cycles of the machines. Thesystem comprises a test wafer, a reader station, and a computer.

The reader station is essentially comprised of an AC power supply,interface circuits between the test wafer and the computer and, ifnecessary a battery charger.

The interface circuits of the reader station are electronic interfacecircuits. The interface circuits of the reader station can benon-contact optical or radio frequency interface circuits.

In a third aspect the present invention provides a method for using arecord of the motion of a wafer, including fine perturbations andvibrations in the motion of the wafer, during its progress through andbetween semiconductor process and inspection machines in the course ofthe actual manufacturing process or in test cycles of the machines todetect, locate, and identify any mechanical malfunction of the machineswhich has caused, or could cause, defects in the manufactured wafer. Themethod comprises the following steps:

-   -   placing the test wafer on the reader station;    -   initializing the test wafer;    -   transferring the test wafer to the processing and/or inspection        machines;    -   recording data relative to the physical history of the wafer in        the internal Flash or other type of memory of the electronics        circuit on the test wafer;    -   returning the test wafer to the reader station;    -   downloading the recorded data into the computer;    -   erasing, if desired, the internal Flash memory of the test        wafer;    -   processing the signals from the accelerometer on the test wafer;        and    -   comparing the recorded data to known data and interpreting the        results.

Initializing the test wafer includes some or all of the steps ofrecharging the battery, downloading different versions of recordingprograms and/or other parameters from the computer into the RAM memoryof the test wafer and initializing the real-time clock.

The signals are processed using the strategies of either on-wafer signalprocessing followed by low sampling-rate signal digitizing or high-ratesignal sampling followed by computer-based signal processing.

The known data to which the recorded data is compared is selected fromeither the precise known time-schedule of events inside the processingmachine and/or “known-good” readings or “fingerprints” of signalspreviously recorded on the same or on similar processing machine.Additionally special software for signal recognition can be used toautomatically detect and interpret “known” problems. For example, if anabnormal signal due to a faulty robot arm bearing presents a specificsignal pattern, it is kept in the computer memory to be automaticallyrecognized in the future.

All the above and other characteristics and advantages of the inventionwill be further understood through the following illustrative andnon-limitative description of preferred embodiments thereof, withreference to the appended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically shows a general diagram of a system according to apreferred embodiment of the invention;

FIG. 2 is a block diagram of the system of FIG. 1, according to apreferred embodiment of the invention; and

FIG. 3 is a block-diagram of the electronic circuits of the test wafer,according to another preferred embodiment of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Although the following description of the invention describes thehandling of semiconductor wafers, it is to be understood that this is inorder to provide an example of the invention which can be extendedmutatis mutandis to related fields such as the manufacturing ofFlat-Panel displays and LCD displays.

FIG. 1 schematically shows a general diagram of the system of theinvention. A typical processing machine 1, as is commonly used in modernsemiconductor plants, is shown in FIG. 1A. Processing machine 1 iscomprised of a unit for inputting the blank wafers 2, a unit for storingthe wafers after processing 3, a number of chambers 5 in which thevarious processes are carried out, and a transfer chamber 4. The wafer 6is moved between the chambers by handling device 7.

FIG. 1B schematically shows the diagnostic station 8 of the system. Itconsists of at least one test wafer 10, a reader station 9, and apersonal computer, or preferably a PC Notebook 11. The test wafers 10are placed in the reader station 9 where they are initialized, then theyare loaded into the processing machine 1 where they will record andstore in a memory unit various measurements relative to the physicalhistory of the wafer as will be explained hereinbelow. After recordingthe measurements, they are returned to the reader station for thedownloading of the recorded data and its interpretation.

In order to measure mechanical impact, the system of the invention makesuse of a test wafer to which a complete miniature electronic recordingsystem is attached. Standard production wafers in modern semiconductorprocessing plants are currently 200 mm in diameter and the industry ismoving towards use of 300 mm wafers. In addition, 6″ (150 mm) wafers arestill popular in older processing plants. For each production wafersize, a test wafer of corresponding size is produced.

In the preferred embodiment of the invention, the test wafers generallyconsist of a standard virgin silicon or aluminum wafer on the surface ofwhich a very thin electronic assembly is attached, e.g. by gluing or anyother suitable means such as use of miniature screws or bolts. Theelectronic assembly is composed of two thin (approximately 0.5 mm)printed circuit boards (PCBs) with a thin rechargeable battery and ofvarious electronic components soldered on one side only of the PCBs. Allelectronic components are low-profile (under 2 mm) surface mountedtechnology (SMT) components. The electronic assembly is then encased ina hermetic thin casing. In other embodiments, the electronics arepositioned on one or more PCBs and/or the test wafers are made ofaluminium or other material tolerable in the clean-room manufacturingenvironment such as gallium arsenide, ceramics, glass, or suitableplastics.

The surface geometry of the test wafers is essentially identical to thesurface geometry of standard production wafers. The attached electronicscauses the weight and thickness of the test wafer to deviate relativelyinsignificantly from the weight and thickness of a standard productionwafer. By way of example, a standard production 8″ silicon wafer mayweigh 50 grams and a 6″ wafer about 30 grams. The PCBs of the preferredembodiment of the invention with all electronic components weigh about15 grams including battery. The test wafer may therefore be handled bythe normal handling equipment of the semiconductor processing machinesin exactly the same way as standard production wafers. Current handlingequipment should normally have no difficulty and should not showsignificant differences in handling even a 50% overweight. In the futurethe 15 grams weight of the electronics will be reduced and the weight ofthe wafer will rise since the industry is adopting 300 mm (12″) wafersas standard.

If necessary, the test wafers can be made exactly identical to standardwafers, in thickness and weight, by first grinding the surface of astandard silicon wafer to reduce its thickness from about 0.7 mm toabout 0.3 mm and then embedding the electronic circuits inside the freedvolume. This can be done on part of the surface, for instance, within acircle centered on the center of the wafer. The electronic componentsare then embedded inside the freed volume and covered by epoxy glue orother suitable means to restore the upper surface to its original level.Wafers produced from other materials can likewise be first made thinnerand lighter than the standard ones in order to get functional testwafers with properties identical to those of the standard wafers.

While it is normally desirable to match the physical characteristics ofthe test wafer to that of production wafers, in some cases it may be ofinterest to deliberately modify the mechanical properties of the testwafers in order to test the handling systems under more extremeconditions. For example, test wafers can be made intentionally heavieror lighter and/or small artificial protrusions or passive wings may bemounted on either face of the test wafer. These wings should be flexibleenough so as not to prevent the displacement of the wafer, yet rigidenough so as to cause a perturbation in the normal movement of thewafer, which will be detected by the accelerometer, whenever the wingscome in contact with external parts. Thus, additional clearance caneffectively be verified along the path of the wafer through theprocessing machine. In some situations, it is advantageous to useelectrically sensitive or active wings in place of passive wings and toconnect their outputs to the electronic circuits of the test wafer.

In a preferred embodiment of the invention, an epoxy block is molded onthe wafer and, attached to the wafer, all around the miniatureelectronic recording system. If it is desired to have access to theelectronic circuits and battery for servicing, a thin hermetic externalcover is mounted above the miniature electronic recording system andattached to the wafer, all around the electronic assembly by suitablemeans such as soldering or gluing. The external cover is of a thicknesssuch that the maximum height of the electronics and cover is preferablyno more than 2 mm and can be made from any material suitable for themanufacturing environment, for example; aluminum, stainless steel,silicon, ceramic materials, composite materials, polyurethane, plastic,etc. This external cover serves to hermetically and thermally isolatethe electronic circuits from the process chamber. Since some metals andmaterials are strictly banned from use in clean-rooms and specificprocess machines, only metals and materials accepted for use in the artappear on the outside of the casing.

The external cover or epoxy mold has several functions and allows theuse of the test wafer under virtually all production conditions:

-   -   1) It allows use of the test wafer in a vacuum, even when some        of the electronic components, such as the battery, may leak        under vacuum conditions. An epoxy mold is the best choice for        isolating the electronics under vacuum conditions.    -   2) The encasing of the electronic assembly protects the process        chamber from pollutants or particles which may originate from        the various parts of the electronic assembly, even under        non-vacuum conditions. The encasing of the battery is especially        important since some batteries, if not hermetically encased, may        leak noxious or otherwise damaging gasses into the process        chamber.    -   3) The external cover provides a certain level of protection to        the electronic assembly from corrosive gases, plasmas or other        hostile conditions which are found in some process chambers.    -   4) The external cover may additionally be designed so as to        thermally isolate the electronic assembly from the surrounding        heat. Thus, the test wafers can be used in hot process chambers,        provided that their stay in these chambers is not of too long a        duration.

When an external cover is mounted over the wafer and the electronicassembly, it is usually advantageous to create a vacuum inside thecover. Thus, under normal atmospheric ambient conditions the uppersurface of the casing is pressed downwards against the internalelectronic components providing sufficient mechanical strength to thetest wafer even when, as is generally the case, the external cover isvery thin. When the test wafer is used in a vacuum environmental, no netforce will be applied on the upper surface since the external andinternal pressures will be similar; if however the volume under theexternal cover is not evacuated, then the internal pressure could resultin rupture of the cover. In addition, vacuum conditions inside the coverprovide improved thermal isolation of the electronics.

Alternatively, if the internal electronic components do not leak undervacuum conditions, venting holes can be made at various locations in thecover of the casing so that the air inside the casing can be evacuatedor restored when the test wafer enters or is removed from a vacuumenvironment.

FIG. 2 is a block diagram of the system of FIG. 1. The PC Notebook 11 isschematically represented on the left and on the right one of the PCBs25 of the test wafer. The reader station 9 electronics essentiallyconsist of an AC power supply 23, electronic interface circuits 21 forthe RS232 serial communication 22 between the PC Notebook 11 and thetest wafer, and battery-charger electronics 24 for the recharging of theinternal battery on the test wafer. The test wafer electronics isequipped with a special external connector 26 which provides fastconnections to the battery 27 and to the serial communication contacts28.

In the presently preferred embodiment of the invention, the readerstation has a receptacle for a single test wafer. The test wafer isseized with a vacuum wand (or with another type of hand accessory asused in the industry) and delicately placed at the correct position andwith the correct angular orientation in the receptacle of the readerstation. When correctly placed, the wafer is positioned with an x-y-zaccuracy of about 0.2 mm (the room left between the wafer and theinternal side of the receptacle). The wafers usually have a “notch” (for8″ and 12″ wafers) or “flat” (for 6″ wafers) on their outer periphery toprecisely mark an angular reference on the wafer. During the mountingoperation of the electronic assembly with its central connector on thetest wafer, the x-y position and the angular position of the electronicassembly and central connector relative to the “notch” or “flat” of thewafer is precisely determined so that all the test wafers have theirelectronic elements similarly positioned and oriented. The receptacle ofthe reader station is designed such that the operator also has to placethe wafer with a precise angular position relative to this notch orflat. In this way, the orientation of the central connector on the waferrelative to the reader station is also precisely determined. Now, theoperator lowers the connector head of the reader station in whichseveral spring-loaded contact probes are mounted. The spring-loadedcontact probes precisely make contact with the corresponding contacts onthe electronics of the test wafer. In other embodiments, the readerstation is designed for several wafers and/or for contactlesscommunication with the Notebook PC and/or incorporates a standard“notch-finder” or “flat-finder” to automatically rotate the wafer to thecorrect angular position.

FIG. 3 is a block-diagram of the electronic circuits of the test wafer.The diagram is generally divided into three parts: the top showing theanalog part of the electronics 31, the middle the digital part 32, andthe bottom the power management part of the electronics 30 and 33. In apreferred embodiment of the invention, 31, 32, and 33 together comprisethe PCB 25 of FIGS. 2 and 30 is a second PCB.

The analog part of the electronics consists of an accelerometer 35,analog processing circuits, and of an analog to digital converter (ADC)36. The accelerometer 35 is a dual-axis accelerometer which is capableof measuring acceleration simultaneously along two orthogonal axes. Theacceleration measured includes constant acceleration forces, such as theearth's gravitational field or prolonged acceleration movements,mechanical shock, perturbations, and vibration. Each output of theaccelerometer is an analog voltage which, when a constant offset voltageis subtracted from it, is proportional to the acceleration along therespective sensing axis. A suitable commercially available sensor foruse in the electronics of the invention is, for example, P/N ADXL202Emade by Analog Devices Inc.

In other embodiments, other types of accelerometers are used includingthose capable of providing 3-axis measurements, higher sensitivity orsignal-to-noise ratio, better response at specific frequencies, orsmaller packaging. One type of accelerometer that is advantageouslyemployed in certain situations is a piezoelectric type such as the Model22 made by Endevco Corporation.

In a preferred embodiment, the ADC 36 includes an analog multiplexerwhich enables the digitizing of eight different analog signals. Theseare, for example, raw signals 37, 38 representing the measuredacceleration of the wafer along the X and Y axis of the accelerometerrespectively, and six other spectral components of these two basicsignals, processed by analog filters 39–42, peak-detectors 43, andsample-and-hold electronic circuits 44. The analog filters in thisembodiment are: 10 Hz low-pass filters 39, 10–100 Hz band-pass filters40, 10–1000 Hz band-pass filter 41, and 1 kHz high-pass filter 42. Asuitable commercially available ADC for use in the electronics of theinvention is, for example, P/N MAX1290AEEI made by Maxim IntegratedProducts.

The digital components of the electronics, shown at 32 of FIG. 3 arecomprised mainly of a microprocessor 50, RAM memory 51 and Flash memory52. A suitable commercially available microprocessor for use in theelectronics of the invention is, for example, P/N DS87C530ENL made byDallas Semiconductor. The DS87C530ENL microprocessor includes, inaddition to standard microprocessor functions, a real-time clock (RTC)53 and 16 kbytes of internal program memory programmed with hardwareinitialization, test routines, and a loader program. Although in thepresently described embodiment of the invention, a Flash memory ispreferred, other types of memory such as RAM are used as the internalmemory to record the signals from the accelerometer in otherembodiments.

Suitable commercially available RAM memory and Flash memory units foruse in the electronics of the invention are respectively, for example,P/N K6T1008V2E and P/N KM29U128IT made by Samsung Electronics. RAMmemory unit 51 consists of data memory 55 and program memory 56subunits. P/N KM29U128IT is a 16 Mbyte Flash memory chip. 64 Mbyte Flashmemory units are now commercially available from Samsung and can beadvantageously used for more recording capacity.

Also shown at section 32 of PCB 25 are external connector 26, whichprovides fast connections to the battery contacts 27 and to the serialcommunication contacts 28, and a LED 54, which gives a visibleindication that the electronics have been activated.

In the bottom part of FIG. 3, is schematically shown the powermanagement part of the electronics. It consists mainly of a rechargeablebattery 60 mounted on a separate PCB 30 and of three DC/DC converterintegrated circuits 62–64 mounted at 33 on PCB board 25.

Suitable commercially available devices for use in the electronics ofthe invention are, for example, SLPB-103462 1 mm-thick Lithium Polymerbattery made by Kokam Engineering Co. (South Korea) and DC/DC converterintegrated circuits LTC1751 and LTC 1516 made by Linear Technology. In apreferred embodiment, the three DC outputs are +3.3V and +5V analog and+5V digital signals. In some embodiments, non-rechargeable batteries areused. Suitable batteries of this type are, for example, energy cellsmade by Power Paper Ltd. (Israel), Ultralife Li/MnO2 Battery P/NU3VF-K-T made by Ultralife batteries Inc. (USA), and Eagle PicherThionyl Chloride Battery P/N LTC-312 made by Eagle Picher TechnologiesLLC (USA).

In addition, two temperature sensors 65 (for example, P/N DS1721 made byDallas Semiconductor) are placed one on each of the PCB boards.

The test wafer's electronics consist of very low-power components andhas a special architecture which permits further significant reductionof the power consumption. All of the circuits of the analog part of theelectronics, shown at 31 in FIG. 3, are switched-off whenever not inuse. Additionally microprocessor 50 enters a special stop mode wheneverno recording is required, keeping only track of time and retainingmemory of all the data and other parameters required in order to wake-upin time to resume recording. Since the wake-up time of themicroprocessor is extremely fast and the wake-up time for theswitched-off electronic circuits is also fast, the microprocessor canusually be stopped between samplings and the circuits at 31 can also bepowered-down, depending on the desired sampling rate. The recording mayalso be stopped according to time-zones programmed into the test waferat the time of initialization or whenever no motion is detected for agiven time period by the on-board accelerometer, in which case it isautomatically resumed when motion is again detected. As a result of theabove, the rechargeable battery provides power for 1 to 10 hours ofactual recording within a time period of one or even several days.

The method of the invention comprises several broad steps. At thebeginning of the recording/diagnostic cycle, the test wafer is placed onthe reader station. There, the battery is recharged, and the real-timeclock (RTC) is initialized by the Notebook PC. The RTC keeps track ofactual time and permits the recording of timestamps along the datarecorded by the test wafer. The microprocessor on the test wafercontains an internal program memory, which is programmed with hardwareinitialization and test routines and a loader program.

By means of the loader program, different versions of recording programsand/or other parameters, e.g. the sampling rate, can be downloaded atthe reader station from the Notebook PC into the RAM memory of the testwafer for subsequent execution.

In the second step, the test wafer is transferred into the processmachine, using the same handling equipment normally used for standardproduction wafers. The test wafer electronics then records all themovements, vibrations, accelerations and other selected physicalparameters imposed upon the wafer during the entire time period that thewafer is within the process machine.

It is to be noted that, once the electronics on the test wafer has beeninitialized, it is capable of measuring all motion of the wafer as it ismoved anywhere, both inside and outside of the various processing andinspection machines, and as it is moved from station to station or evenbetween rooms in the production plant. In addition, the electronics onthe test wafer records, and can be used to identify, vibrations andshocks that are caused by other elements in the processing environmentthat are not directly connected to the test wafer such as valves, motorsand pumps.

When the wafer is recording the signals from its accelerometer in anatmospheric environment, it functions much as a large ear and detectsand records—in addition to the movements of the wafer itself—any noisewhich is “heard” nearby. In a vacuum its “hearing” capabilities arelimited to—in addition to the movements of the waferitself—perturbations and vibrations transmitted by the mechanic elementsholding the wafer. The “hearing” capabilities of the test wafer arenonetheless appreciable even in this case and can reach to remoteelements which will be of interest to the user. The data described aboveis also strictly time-related to the sequence of events recorded by thetest wafer and therefore analysis of the performance of remote elements,which might be otherwise difficult to analysis under real conditions,can be accomplished using the device and method of the invention.

The data is recorded in the internal Flash memory of the electronicscircuit on the test wafer, which has enough capacity for many hours ofcontinuous recording under a moderately-low sampling rate.

In the third step, the test wafer is returned to the reader station. Therecorded data is then downloaded into the Notebook PC. Subsequently, theinternal Flash memory of the test wafer can be erased if desired and thetest wafer is ready for a new sequence of recording. If the remainingcharge of the internal battery is insufficient, then the battery must berecharged before reusing the test wafer.

In some embodiments of the invention, communication not involvingphysical contact between the Test Wafer and the MEA reader isadvantageously used. For instance optical transponders with infrared orvisible light LEDs and detectors are mounted on the test wafers withmatched LEDs and detectors on the reader. In this way, fast download canbe performed for a full batch of test wafers concurrently, and, contactwith, and possible damage to, the wafers is avoided. In this case, anon-contact recharging technique is also used for the battery.Alternatively, non-rechargeable batteries are used or the rechargeablebatteries are recharged only at other occasions. In other embodimentsradio frequency (RF) techniques are used to transfer information betweenthe test wafer and the reader.

Finally, the signals recorded by the test wafer are interpreted by theNotebook PC or by another computer to which the data is transferred.

As described hereinabove, a miniature accelerometer is incorporated inthe electronic circuits of the test wafer. It is the output signals ofthe accelerometer, which are accurately recorded and stored in the testwafer's internal memory that must be analyzed at this stage. Theminiature accelerometer used in the test wafer is very sensitive (orderof resolution 1 milli-g over a full-scale range of ±2 g) and has afrequency response ranging from DC to over 6 kHz. In order to fullyexploit the signal from the sensor, one of two basic signal-processingstrategies can be chosen.

The first strategy involves on-wafer signal processing followed by lowsampling-rate signal digitizing. This strategy is illustrated in theimplementation of the test wafer electronics described with reference toFIG. 3. The X-raw and Y-raw signals are filtered by low-pass, high-pass,and band-pass filters followed by peak detectors and sample-and-holdcircuits. The output of the low-pass filters is sampled at a relativelylow rate (e.g. 64 Hz) and conveys a time-related description of thebroad movements of the wafer (translation, rotation, elevation etc.).The output of the high-pass and band-pass filters is processed bypeak-detector and sample-and-hold circuits, and then sampled at asimilarly low rate. They convey shock and vibration information which istime related to the low-pass data and can be interpreted to reveal theseverity of the shocks and vibrations and to identify the origin of themechanical perturbations. At the end of the recording session the testwafer is returned to the reader station and the recorded data isdownloaded into the PC Notebook.

The second strategy consists of high-rate signal sampling followed byPC-based signal processing. Using this strategy, the two outputs of thesensor X-raw and Y-raw, i.e. the unfiltered signals of the sensedacceleration along the X-axis and the Y-axis of the accelerometerrespectively, are digitized at a high sampling-rate of several kHz (notethat according to the Nyquist criterion, at a typical sampling rate of12 kHz, up to 6 kHz of signal bandwidth can be recovered. The electroniccircuits of the test wafer permit a sampling rate of over 50 kHz andthus permit the recording of signals extending to over 25 kHz). Theanalog filters, peak detectors and sample-and-hold circuits shown inFIG. 3 are not used in this case.

At the end of the recording session, the test wafer is returned to thereader station and the recorded data is downloaded into the PC Notebook.The data is then processed by the PC or another computer usingappropriate digital filtering techniques in order to separate andanalyze the various spectral components of the X-raw and Y-raw signalsas a function of time for the duration of the recording session. Forthis purpose, standard signal processing software can be used such as inthe Labview Signal Processing Toolkit sold by National Instruments. Thissecond strategy offers more versatile and precise analysis of theaccelerometer's signals, but it requires more battery power and memorycapacity per recording hour than the first strategy.

In both cases, the recorded data is available for display on theNotebook's screen right after having been downloaded from the testwafer. Separate graphs may be displayed, some representing the broadmovements of the wafer and others the occurrences of shocks orvibrations. All graphs have a common time scale. The data can thereforebe related to the precise known time-schedule of events inside theprocessing machine, which can usually be downloaded in the form of adata file from modern semiconductor processing machines. Additionally,the user may have at his disposal a number of “known-good” readings or“fingerprints” of signals previously recorded on the same or on similarprocessing machine. With these, the user will have the means to identifythe successive handling stages of the wafer inside the machine and todetect, measure, and diagnose any abnormal events, i.e. scratches,shocks, or vibrations, which could damage the wafer. Since theoccurrence of abnormal events is detected and time-stamped, the locationand cause of mechanical failures can accurately be established andtracked. With the use of additional special (learning) software forsignal recognition, “known” failures are automatically detected andinterpreted by the computer. For example, if an abnormal signal due tofaulty robot arm bearings presents a specific signal pattern, thispattern is kept in the computer memory to be automatically recognized inthe future.

The test wafers can be used in various ways. As part of ordinarypreventive maintenance activities they are introduced into the processmachine and serve to verify that the handling of the wafers isfault-free. The test wafers can also be used during production fortroubleshooting a machine with a high rate of defects or breakageproblems. Tests can be conducted either whenever a doubt arises or atgiven periodic time intervals. Several test wafers can be introducedinto the process machine simultaneously in order to speed up the testprocedure. This is particularly important since some failures may occuronly intermittently or, in cases in which each wafer has a differentroute inside the process machine, only for one specific wafer out of afull batch.

By way of illustrating the application of the method of the invention,suppose that a person in charge of the wafer handling inside a specificmachine wants to make sure that wafers do not touch any other mechanicalparts inside the machine when being transferred from point A to point B.Employing the known procedure of the prior art, he would disassemble themachine. Apart from time required and cost expended, he would not beable to see the machine working in its real conditions, nor could hesimulate vacuum or other environmental conditions.

Using the system of the invention, he loads one or several test wafersinto the machine. After a short wait the test wafers automatically exitthe machine. The data is now downloaded into the PC Notebook and theoccurrence of any contact of the wafer with any part of the machine canbe determined by either comparing the newly obtained graphs to“known-good” graphs previously recorded on the same machine and/or bycomparing the timing of the main events to the time-schedule of eventstaking place within the machine.

Assuming that the transfer of the wafer from point A to point B isabsolutely smooth and vibration-free in the “known-good” graphs, anydisturbance in the new graphs between the time points identified aspoint A and point B will signal an abnormal condition which can becharacterized and tracked down. Assuming that the transfer from point Ato point B involves some vibration or humming in the “known-good”graphs, these normal reference signals can be subtracted from the newgraphs and abnormal signals highlighted.

It will be appreciated by those skilled in the art that all of theseoperations, including synchronization, filtering, comparing, featureextraction, and analysis can be automatically performed by the PCNotebook using ad-hoc programs and algorithms.

The skilled person will recognize that additional sensors may also beused to identify the exact position of the test wafer as a function oftime not only to identify the position of the wafer but also to providevaluable information on actual physical conditions inside the processingchambers. For example, in the preferred implementation discussedhereinabove are included two temperature sensors mounted inside theexternal cover of the test wafer. Additional temperature sensors can beplaced on the outside of the enclosure with high temperature measurementcapability in order to map and record the true temperature distributionon the surface of the wafer at various locations and under variousprocess conditions. Likewise, appropriate miniature sensors mounted onthe test wafer can be added in order to test, map and record otherphysical parameters inside the process chamber such as light, pressure,air-flow, gas-flow, humidity, clearance (using, for example,ultrasound), electric and magnetic fields. For instance, light sensorswith selective sensitivity in the UV portion of the light spectrum canbe used to check actual plasma light glow conditions inside the processchamber. In addition a miniature camera can be mounted on the test waferand the images it gathers recorded in the Flash memory with the rest ofthe data. Using the method described above the exact location of thetest wafer at the time the data from any of these sensors is recorded isprecisely determined providing additional valuable information foranalyzing the production process. This data can also be used to measurethe air flow along the wafer route between machines to determine if andwhere any deviations from laminar flow occur. This information is vitalfor keeping the airborne particle level low in the so-called“mini-environment” processing environment.

Although embodiments of the invention have been described by way ofillustration, it will be understood that the invention may be carriedout with many variations, modifications, and adaptations, withoutdeparting from its spirit or exceeding the scope of the claims, inparticular the invention can be extended mutatis mutandis to relatedfields such as the manufacturing of Flat-Panel displays and LCDdisplays.

1. A system for detecting, identifying, and locating any mechanicalmalfunction, which has caused, or could cause, defects in a wafermanufactured by semiconductor process and inspection machines in thecourse of the actual manufacturing process or in test cycles of saidmachines, said system comprising: a test wafer, comprising a miniatureelectronic recording system, which comprises at least one accelerometerand circuitry for recording data that characterizes the motion of saidtest wafer, including fine perturbations and vibrations in its motionduring its progress through and between said semiconductor process andinspection machines; a computer, comprising: software for initializingand downloading recorder programs to said miniature electronic recordingsystem before said test wafer is placed in said semiconductor processand inspection machines; software for transferring said data thatcharacterizes the motion of said test wafer from said miniatureelectronic recording system to said computer; known data, whichdescribes the “known good” behavior of a wafer during its progressthrough and between said semiconductor process and inspection machines;and software for detecting, identifying, and locating said mechanicalmalfunction; and a reader station, comprising an AC power supply,interface circuits between said test wafer and said computer, and, ifnecessary, a battery charger; wherein; said recorder programs cause saiddata that characterizes the motion of said test wafer to be recordedalong the entire path of said test wafer through and between saidsemiconductor process and inspection machines; and said software fordetecting, identifying, and locating said mechanical malfunctiondetects, identifies, and locates said mechanical malfunction bycomparing said recorded data that characterizes the motion of said testwafer with said known data.
 2. The system according to claim 1, whereinthe test wafer is selected from the group comprising: wafers whosesurface area and, shape, thickness, and weight are essentially equal tothose of standard size production wafers; and wafers whose surface areaand shape are essentially equal to those of standard size productionwafers but whose thickness and/or weight differ from those of standardsize production wafers.
 3. The system according to claim 2, wherein thetest wafer is made from a material selected from the group comprising:silicon; aluminum; glass; gallium arsenide; ceramic material; andplastic.
 4. The system according to claim 1, wherein the miniatureelectronic recording system is attached to the test wafer by meansselected from the group comprised of: gluing; screwing; and bolting. 5.The system according to claim 1, wherein the components of the miniatureelectronic recording system are mounted on one or more circuit boards.6. The system according to claim 1, wherein the miniature electronicrecording system is covered by an epoxy block molded on the wafer. 7.The system according to claim 1, wherein a thin hermetic external coveris mounted over the miniature electronic recording system and isattached to the wafer.
 8. The system according to claim 7, wherein thehermetic thin casing has a thickness such that the maximum height of theelectronics and cover is preferably no more than 2 mm.
 9. The systemaccording to claim 7, wherein the hermetic thin casing is made of amaterial chosen from the group comprised of: aluminum; stainless steel;composite materials; polyurethane; silicon; ceramic materials; andplastic.
 10. The system according to claim 1, wherein the miniatureelectronic recording system additionally comprises components selectedfrom the group comprised of: analog-to-digital converters;microprocessors; batteries; memory units; temperature sensors; analogmultiplexers; analog filters; peak-detectors; and sample-and-holdelectronic circuits.
 11. The system according to claim 1, wherein theaccelerometers are selected from the group comprised of: dual-axisaccelerometers; 3-axis accelerometers; and piezoelectric accelerometers.12. The system according to claim 10, wherein the analog-to-digitalconverter includes an analog multiplexer, which enables the digitizingof a multitude of analog signals.
 13. The system according to claim 10,wherein the microprocessor includes a real-time clock and internalprogram memory.
 14. The system according to claim 10, wherein thebattery is a rechargeable battery.
 15. The system according to claim 14,wherein the rechargeable battery is a lithium polymer battery.
 16. Thesystem according to claim 10, wherein the memory unit is composed of RAMmemory and/or Flash memory.
 17. The system according to claim 1, whereinadditional sensors are attached to the test wafer, said sensors beingsuitable to measure parameters selected from the group comprised of:temperature; light; pressure; air-flow; gas flow; humidity; clearance;electric field; and magnetic field.
 18. The system according to claim 1,wherein a miniature camera is attached to the test wafer.
 19. The systemaccording to claim 1, wherein the miniature electronic recording systemdetects the motion of the test wafer to which it is attached and usesthe presence or absence of said motion to switch off or wake up saidelectronics in order to conserve power.
 20. The system according toclaim 1, wherein the interface circuits of the reader station areelectronic interface circuits.
 21. The system according to claim 1,wherein the interface circuits of the reader station are non-contactinterface circuits.
 22. The system according to claim 21, wherein thenon-contact interface circuits of the reader station are opticalinterface circuits or radio frequency interface circuits.
 23. A methodfor using a record of the motion of a test wafer, including fineperturbations and vibrations in the motion of said wafer, during itsprogress through and between semiconductor process and inspectionmachines in the course of the actual manufacturing process or in testcycles of said machines, to detect, identify, and locate any mechanicalmalfunction of the processing machine which has caused, or could cause,defects in the manufactured wafer, comprising the following steps:placing said test wafer on the reader station; initializing said testwafer; transferring said test wafer to said processing machine;operating said processing machine under normal operating conditions;recording, in the miniature electronic recording system mounted on saidtest wafer, data from at least one accelerometer, said datacharacterizing the motion of said test wafer; processing the signalsfrom the accelerometer on said test wafer; returning said test wafer tosaid reader station; ownloading said recorded data into a computer;erasing, if desired, said data recorded in said of said miniatureelectronic recording system; and detecting, identifying, and locatingany mechanical malfunction of the processing machine; wherein; said datathat characterizes the motion of said test wafer is recorded along theentire path of said test wafer through and between said semiconductorprocess and inspection machines; and the software of said computerdetects, identifies, and locates said mechanical malfunction bycomparing said recorded data characterizing the motion of said testwafer with known data previously stored in the memory of said computer.24. The method according to claim 23, wherein initializing the testwafer includes some or all of the following steps: recharging a batteryon said test wafer; downloading different versions of recording programsand/or other parameters from the computer into the memory of said testwafer; and initializing the real-time clock on said test wafer.
 25. Themethod according to claim 23, wherein the signals are processed usingone of the strategies selected from the group comprising: on-wafersignal processing followed by low sampling-rate signal digitizing; andhigh-rate signal sampling followed by computer-based signal processing.26. The method according to claim 23, wherein the known data to whichthe recorded data is compared is selected from the group comprising: theprecise known time-schedule of events inside the processing machine; and“known-good” readings or “fingerprints” of signals previously recordedon the same or on similar processing machine.
 27. The method accordingto claim 23, wherein comparing the recorded data to known dataadditionally comprises the use of special software for signalrecognition to automatically detect and interpret “known” problems.